Nanoscale covalent organic frameworks for enhanced photocatalytic hydrogen production

Nanosizing confers unique functions in materials such as graphene and quantum dots. Here, we present two nanoscale-covalent organic frameworks (nano-COFs) that exhibit exceptionally high activity for photocatalytic hydrogen production that results from their size and morphology. Compared to bulk analogues, the downsizing of COFs crystals using surfactants provides greatly improved water dispersibility and light-harvesting properties. One of these nano-COFs shows a hydrogen evolution rate of 392.0 mmol g−1 h−1 (33.3 μmol h−1), which is one of the highest mass-normalized rates reported for a COF or any other organic photocatalysts. A reverse concentration-dependent photocatalytic phenomenon is observed, whereby a higher photocatalytic activity is found at a lower catalyst concentration. These materials also show a molecule-like excitonic nature, as studied by photoluminescence and transient absorption spectroscopy, which is again a function of their nanoscale dimensions. This charts a new path to highly efficient organic photocatalysts for solar fuel production.

Editorial Note: This manuscript has been previously reviewed at another journal that is not operating a transparent peer review scheme.This document only contains reviewer comments and rebuttal letters for versions considered at Nature Communications.

REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): The revised manuscript by Zhao et al. reflects improvements based on reviewers' feedback, including necessary explanations and additional characterizations like solid-state 13C NMR, XPS analyses, etc.These enhancements have rendered the manuscript well-organized and scientifically robust compared to the initial submission.Given its novelty and scientific content, the manuscript is deemed suitable for publication, with attention to minor concerns: 1.The N2 adsorption and desorption profiles of TFP-BpyD nano-COF should be reevaluated, particularly focusing on the micropore region (Supplementary Figure 9), to ensure accurate pore size analyses.
2. The manuscript should incorporate the rationale behind selecting ascorbic acid (AA) as a sacrificial electron donor.This addition will enrich the contextual understanding of the experimental approach.
Addressing these minor concerns will further strengthen the manuscript and ensure its alignment with publication standards of "Nature Communications".

Comments for Reviewer #2:
The manuscript from Zhao et al. has undergone revisions based on the feedback from the reviewers.In response to suggestions, the authors have made several improvements, including: -Providing a list of other organic photocatalysts alongside representative pristine COFs in Table S3.
-Explaining the reason for the photoluminescence (PL) intensity quenching with increasing concentration (Supplementary Figure 47).
-Revising the captions of Supplementary Figure 46 and adding diffraction indices for each peak in Supplementary Figures 17 and 18.
-Assigning all vibration frequencies of each band in the Fourier-transform infrared spectroscopy (FT-IR) in Supplementary Figure 16.-An explanation of the two PL emission bands is provided in Figure 3b.
-Describing the mode of operation and radius of curvature of the tip in atomic force microscopy (AFM) analyses.
-Enhancing the quality of figures and revising references.These changes have significantly improved the quality and suitability of the manuscript for publication in Nature Communications.Thus, the manuscript could be accepted for publication in its current form.

Reviewer #2 (Remarks to the Author):
The authors submitted the revised manuscript "Nanoscale Covalent Organic Frameworks for Enhanced Photocatalytic Hydrogen Production" The reviewer believes that this manuscript is not suitable to publish in this journal.1.The morphology of TFP-BpyD nano-COF and TFP-BD nano-COF are unclear in the TEM and AFM.In addition, all these materials are reported before.2. There is a mistake in Figure 1. 3. the reviewer believes these two COF materials have no fluorescence properties or weak emission.how about their quantum yields?4. The solid-state NMR, FT-IR, NMR, SEM, and BET of TFP-BpyD nano-COF and TFP-BD nano-COF after the photocatalytic reaction to further ensure its stability.5.The manuscript title is unclear and not interesting to journal readers.6.The reviewer didn't see any data about the apparent quantum yields for these materials and real photos of H2 bubbles of these materials.

Reviewer #1 (Remarks to the Author):
The revised manuscript by Zhao et al. reflects improvements based on reviewers' feedback, including necessary explanations and additional characterizations like solid-state 13C NMR, XPS analyses, etc.These enhancements have rendered the manuscript well-organized and scientifically robust compared to the initial submission.Given its novelty and scientific content, the manuscript is deemed suitable for publication, with attention to minor concerns: 1.The N2 adsorption and desorption profiles of TFP-BpyD nano-COF should be re-evaluated, particularly focusing on the micropore region (Supplementary Figure 9), to ensure accurate pore size analyses.

Response:
We thank the reviewer for this comment.We have now re-measured the N2 sorption focusing on the micropore region.Supplementary Figure 1  2. The manuscript should incorporate the rationale behind selecting ascorbic acid (AA) as a sacrificial electron donor.This addition will enrich the contextual understanding of the experimental approach.
Following the reviewer's suggestion, we have now provided a rationale for the selection of AA as a sacrificial electron donor in the revised manuscript as follows: "Here, we selected ascorbic acid (AA) as a sacrificial electron donor because of its strong reducibility for ketoenamine COFs, as evidenced by previous work 18 ".Addressing these minor concerns will further strengthen the manuscript and ensure its alignment with publication standards of "Nature Communications".: has been updated as follows: Supplementary Figure 2. N2 adsorption and desorption profiles at 77.3 K (left), pore size distribution profile calculated by DFT (center) and BET surface area plot derived from N2 sorption isotherm of TFP-BpyD nano-COF (right).